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What's the Trade-off with High Gain?  

post #1 of 10
Thread Starter 
I'll limit this question to the Draper M2500 unless someone objects. The widespread enthusiasm for that material has me wondering just what drawbacks it may have for CRT projection.

Tim in another post said:

"...I use the M2500 screen. Since I got the Crystalimage processor I lowered the brightness and contrast somewhat over what I had it set at with the DVDO iScan...
I like the lower brightness/contrast, blacks are black and there is better detail.
Too much brightness in a video image tends to give me headache after a short while in a totally dark room..."


Is the High gain (now 2.1?) Draper M2500 screen prone to reduce detail in a trade-off for brighter colors and higher contrast?

Does it have other flukes or drawbacks or is this really the stuff Dreams are spun with?

High gain screens are also said to increase the visibility of hot spotting - presumably not by adding this effect but by revealing any existing projected hot spots due to their greater reflectivity.

But can one not use high gain and compensate with lower projector (CRT) settings - thus increasing all at once screen size, tube longevity, and maybe even image quality?

Thanks for your feedback...our former losses contribute to our future high gains!


[This message has been edited by Brett (edited January 17, 2000).]
post #2 of 10
Thread Starter 
Alright Brett,

I guess I'm feeling sorry for you not getting any answers over the past couple of weeks.

So here's my best shot:

High gain has no more trade offs than any other level of gain screens.
It is all a matter of balance, balance between screen size, projector type, projector brightness, projector mounting height, viewing angle, incident light...

It is also a matter of preference, preference for brighter colors, crisper contrasts, bigger screens, more perceived depth, versus preference for totally accurate colors, wider viewing angle and freedom from hotspotting.

By the way, have the vertical streaking problems with Draper's M2500 high gain screen been solved yet, or at least acknowledged by the Manufacturer???

Best of luck in your quest.
post #3 of 10
Thread Starter 
Thanks Stevie,

Your post is cristal clear.

I knew of hotspotting, but spectral light distorsion doesn't sound like a very pleasant side effect of high gain.

Do you know which wavelengths get distorted worse (does each CRT tube's light output get the same type amount of distortion) or are some sections of the spectrum more hardly hit?

And at which level of gain does this become noticeable? 1.1 - 1.3 - 1.5 - 1.8 ?

Thanks for your insights.


post #4 of 10
Hi Brett...

That question can depend on the brightness of your projector if/when you will or will not see the hot spot issue.

The CRT issue tht Stevieng is speaking of for expample can be almost removed by the NEC XG line of projectors. They have the programming to allow a blending of the crts across the screen surface. I have Drapper M2500 and when I had my XG135, it was not noticable.

Now...I just put in a DWIN HD700. Now I have an issue. I do see this problem with one side of my screen being 'hot' and the other 'cold' (Red and Blue guns). This is because of the screen gain and the brightness of the CRTs. I also can not do the NEX XG blend trick.

The currenly shipping M2500 is a 2.3 gain. Also needed to note is that Draper does not use any "Spray On" reflective to add gain. The use of a spry on reflective can result in a twinkle affect or hot spotting in screen sections that might have received too much reflective. The M2500's reflective quality is from the material itself. The 'vertical streaking' issue is not on all screens.

The use of a high gain screen, the M2500, resulted in better contrast and blacks for me. It just made the image come alive. I am now waiting for a Draper M1300 to replace my M2500 to correct for the brightness of the DWIN projector. I suppect it will be of the same high quality I am come to like from my M2500 and Draper.

David Bott
It's A World Of Entertainment...Experience It!
AV Science Webmaster
post #5 of 10
Thread Starter 

First I'd like to commend you and Alan for the ultimate in HT boards.

And thanks for your most instructive post regarding the distinguishing characteristics of NEC CRT projectors.

Had I only known earlier! I just bought a 9" Sony (no CRT blending on a 1292) and probably would have gone with one of AV Science's refurbished NECs that have this unique capability.

Maybe you should "sell" this point on the CRT forum as it would be instructive to those making a choice between brands of used or refurbished CRT projectors.

Howevern in this thread your comments about the vertical streaking on the M2500 Drapers have me puzzled:

Could it be a random phenomenon due to manufacturing processes (once in a while it doesn't gel quite right), or is it due to recent changes in the chemical composition of the material?

I guess if it is a random problem, one can always take a chance, but if not, wouldn't it be better to wait for Draper to sort things out?

I don't mean to corner you here into taking a semi-official position regarding one of your suppliers. Even if you can't respond directly, would you recommend I wait a while or do you also sell Stewart screens?


Would that mean that I wouldn't get "any" or minimal hotspotting with a Stewart Videomatte 200? I am sure it is much more expensive than the Draper M2500 which has some noticeable yet not overly disturbing (by most accounts) hotspotting with cieling mounted CRT projectors.

Have you seen either screen in use?
Do you know if one can find a chart showing their respective color response and color linearity?

Also, as you are infused with authoritative HT science, do you know what may be causing the phenomenon of "vignetting" experienced by those using Draper M2500?
(see Bob & Fred's posts in the "High Gain Shootout" thread in the screen forum)

Thanks to both for your helpful posts.


post #6 of 10
Thread Starter 

Thanks for your post. Is your NEC cieling or floor mounted? I have a (possibly incorrect) suspicion that the Draper M2500's vertical streaking might be more apparent with floor mounted setups...

In any case, your experience testifies that it is not a recent problem due to changes in chemical formulation.

We all wish Draper would face the issue and come clean with clear instructions as the optimal use of this otherwise excellent screen (projector type, mounting configuration...) if potential streaking is something that can be determined prior to purchase.

I'm glad you will be looking into German screens. I am already looking at screens from 2 French manufacturers to see if anything seems promising among their high gain models.

If any look good, I'll post them here.
And if you find a "well engineered" German product, I always enjoy opening up my engine on the Autobahn...(naw - it ain't a Porsche).


post #7 of 10
Thread Starter 

Thanks for your post.
Do you mean that you actually view films without the blocking light from your windows? Or is it just due to residual light peeking out around the edges of drapes & curtains?

Does this allow you to use extremely low brightness and contrast settings? Is the spectral balance respected? How natural are the colors and how realistic is the reflected image (impression of looking at a real scene rather than just at a precise image)? Can you view Black & White films without any screen coloration?


Sorry if my post seemed cryptic. There was no intended irony, only respect for what as a newbie has helped confer a better understanding of principles which are new to me.

I can't imagine how anyone could be in the least offended by your very fine posts, and just meant to highly praise your analysis of screen reflection phenomena - and certainly in no way cast even a shadow of a doubt on your insight or abilities. I'll have to be more direct in my compliments next time around. Hope this cleared things up.

Regarding your experience with Stewart's Videomatte 200 (finally a user testimonial!!!), am I correct in assuming that hotspotting would be worse the closer the projector is to the screen, and yet worse the larger the screen is because one would have to raise the brightness accordingly?
Thanks for your candid opinion. (no more of that HT lore jargon...sorry)

I had been quite impressed with the clarity of your previous posts, and assumed that you probably held the key to what still remains for me a mystery: vignetting (brighter at center than at sides of the screen)

I wonder if it is due to respective distance to a centered projector and the related differential in brightness, and if this is accentuated as screen gain increases?


post #8 of 10
Thread Starter 

I'm sorry you've got such an annoying streaking problem. It confirms that any projection is only as good as its reflective support...

Have you tried lowering the effective gain with masking rings on your CRTs? It may make no difference or could even worsten things, but its a quick tweak and just about as free as they get, and who knows - it may just help reduce the streaking some. See Bob's posts (threed123) in this thread.

Sorry that all I can provide is a "desperate suggestion"...


I'm very interested in the fact that a 1292 can produce good results with a curved screen. With respect to your experience, could you say whether the following concern is justified?

(from thread: http://www.avsforum.com/ubb/Forum9/HTML/000178.html )

"I`m a bit more hesitant about the curved screen today, because I was told that you`ll get noticeable distortion during panning."

Also, did you use your 1292 with another screen before the curved one, and what are their respective pros and cons?

Thanks for your helpful feedback!


post #9 of 10
Thread Starter 

Thanks for sharing your candid assessment of the Draper screen. As to the Draper's frame structure, it is possible that in Germany you have been accustomed to such a high level of engineering design excellence that your expectations are higher than those of average Joe HT enthusiasts such as myself?

Also, I've heard some very positive appreciations of Draper's M2500 used with no visible streaking, so some of these screens must exist without that problem. But buying one would be quite a gamble for those of us in Europe, where "no questions asked" return policies are unheard of and where it is virtually impossible to test an item prior to its purchase (especially when shipped from overseas).

I'm in contact with the folks at Vutec - who are said by other members here to be somewhat better positioned - with respect to their pricing - than other screen manufacturers.

I've heard some good things about some of their screens, and will be trying to view samples or full screens in the weeks to come.

Obviously, I'll post any observations I might have, keeping in mind that I am a newbie, and that my untrained eye will probably miss numerous testing parameters!

Regarding the masking technique, it will lower the total amount of light emitted from your lenses and will thus proportionally lower the resultant luminosity of your screen. You can compensate by upping your CRT brightness (not recommended if it drives your tubes too hard) or adjust your viewing expectations to a less bright image if your overall satisfaction is thus increased.

While it should somewhat reduce the intensity of hotspotting as the amount of light hitting the screen is decreased and - who knows how or why - it could impact streaking? Keep us posted as to the effect of CRT masking on observable M2500 streaking even if you plan to change screens, as lots of others here are affected by it...



post #10 of 10

Now I am concerned. I was considering adding a Draper M2500 screen to my home theater as a replacement for my present screen. I have a Dwin HD-700. Are you saying that in your expert opinion you would not recommend the M2500. Is the color shift that noticeable and/or annoying? It this increased gain still worthwhile with that screen with a HD-700 (My screen would be 114" Diagonal, 1.85)
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